Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
Case	Tag   Price	Sales   Tax %	Raw Total   Incl. Sales Tax	Rounded   to Penny	Rounded   to Nickel	Rounded   to Dime
Purchase #1	$232.41	10.791%	$257.4894	$257.49	$257.50	$257.50
Purchase #2	$132.68	9.577%	$145.3868	$145.39	$145.40	$145.40
Purchase #3	$186.38	7.749%	$200.8226	$200.82	$200.80	$200.80
Purchase #4	$130.96	3.728%	$135.8422	$135.84	$135.85	$135.80
Purchase #5	$97.61	3.167%	$100.7013	$100.70	$100.70	$100.70
Purchase #6	$145.84	8.702%	$158.531	$158.53	$158.55	$158.50
Purchase #7	$82.50	3.733%	$85.5797	$85.58	$85.60	$85.60
7 purchase totals =	$1,008.38		$1,084.3530	$1,084.35	$1,084.40	$1,084.30